This invention relates to a pipe coupling and to a pipe joint formed from the pipe coupling.
Mechanical couplings for coupling together pipes formed from plastics materials such as polyolefins and polyvinyl chloride are well known. Such couplings typically comprise a sleeve, a compression collar, a seal disposed axially between the sleeve and compression collar and means (e.g. a compression flange and flange bolts) for compressing the compression collar against the seal to deform it radially inwardly and into sealing contact with the pipe. In addition, it is customary for the coupling to contain a gripping ring or other gripping element to prevent the pipe from being pulled out of the coupling.
A problem with such mechanical couplings is that unless the end of the pipe is supported, it can collapse under compression by the sealing assembly. Consequently, it is usual to place a cylindrical supporting member, e.g. formed from a stiffer plastics material or a metal, within the bore of the pipe end, to prevent the pipe end from collapsing when compressed. Such supporting members are, however, considered undesirable for several reasons. For example, the bore upset caused by the presence of the supporting member can interfere with the flow properties of the pipe, particularly with viscous materials or fluids containing solids. With more abrasive fluids such as slurries, any reduction in the pipe bore can cause increased wear and erosion of the pipe wall and supporting member.
A further problem with conventional pipe couplings is that the time taken to tighten a large number of flange bolts to the torque necessary to achieve a good seal between the pipe, gasket and seal can be considerable. It would therefore be advantageous if the number of flange bolts could be reduced, and the torque needed to achieve an efficient seal reduced without any loss of seal integrity.
A still further problem is that conventional pipe couplings of the type mentioned above are not suitable in many cases for use with pipes formed of more brittle materials such as clay, and this is due to the high compressive forces applied to the pipes to achieve an efficient seal which, if applied to brittle pipes could lead to pipe collapse or fracture.
Attempts have been made by the present inventors to obviate the need for the supporting inserts by using pressure responsive sealing systems such as lip seals and O-rings. However, both approaches present additional problems. In the case of O-rings, it can be very difficult in practice to insert a pipe through a seal without using tremendous force, which can often be beyond the capability of one person, or even two people, without special tools. In the case of lip seals, whilst they are easier to install on the pipe, it is not possible to assemble the pipe coupling wholly on one pipe to enable repair sections to be inserted, nor is it possible to allow the last connection to be made between two plain ended sections of pipe.
It is an object of the present invention to overcome the aforementioned problems and to provide a pipe coupling for plastics pipes in which the use of supporting inserts can be avoided without compromising the integrity of the seal.
Accordingly, in a first aspect, the invention provides a pipe coupling for attachment to a pipe, the coupling comprising a sleeve, at least one end of which is configured to receive therein an end of the pipe; annular sealing means disposed within the end of the sleeve for encircling the pipe end; and compression means for compressing the annular sealing means to form a seal between the pipe and the sleeve; characterised in that the sleeve and/or the sealing means are configured so as to define a leak path between an axially inner portion of the sealing means and the inner surface of the sleeve whereby in use pressurized fluid from the pipe may pass along the leak path so as to pressurize a radially outer surface of the sealing means and urge the axially outer sealing means against the compression means and the axially inner portion of the sealing means against the pipe thereby to enhance the seal between the sealing means and the sleeve, and the sealing means and the pipe.
The pipe couplings of the invention are particularly suited for coupling together plastics pipes and pipes formed from materials which can break or distort such as clay and concrete. Particular examples of plastics pipes which can be connected together using the couplings of the invention include pipes formed from a polyolefin (such as polyethylene) or polyvinylchloride. It has been found that by providing a leak path between the axially inner portion of the seal and the sleeve such that an axially outer portion of the sealing means is compressed against the compression means and the axially inner portion of the sealing means is compressed against the pipe, an effective seal can be formed at a much lower compression force. This in turn means that it is possible to omit the supporting or reinforcing inserts typically used to prevent the collapse of the ends of plastics pipes when coupled together using mechanical couplings. Moreover, in the case of pipes formed from brittle materials such as clay, significantly lower compressive forces can be applied to the gasket without reducing the integrity of the seal, thereby reducing the risk of the pipe breaking under compression.
In this specification, the terms xe2x80x9caxially outerxe2x80x9d and xe2x80x9caxially innerxe2x80x9d are used to denote to denote the positions of elements relative to the mid point of the sleeve. An element described as xe2x80x9caxially outerxe2x80x9d is further from the mid point of the sleeve than an element described as being xe2x80x9caxially innerxe2x80x9d. Thus the axially outer portion of the sealing means is further from the mid point of the sleeve than the axially inner portion.
The term xe2x80x9cradially innerxe2x80x9d as used herein with regard to the sealing means refers to a portion or surface which faces the pipe, whereas the term xe2x80x9cradially outerxe2x80x9d refers to a portion or surface which faces the sleeve. The terms are not intended to mean that the surfaces or portions in question are parallel to the axis of the pipe, although in certain circumstances they may be.
Underlying the present invention is the recognition that by forming a leak path between an axially inner portion of the sealing means and the inner surface of the sleeve, the seal can be made at least partially pressure-responsivexe2x80x94i.e. the pressure of fluid in the pipe can be used to compress the sealing means against the sleeve and the pipe thereby enhancing the strength of the seal.
Either the sleeve or the sealing means, or both, may be configured to provide the leak path. The leak path is typically defined by means of channels formed between the sealing means and the sleeve. Thus, for example, the sleeve may be provided with one or more grooves in the surface thereof which by-pass the axially inner portion of the sealing means. Although one groove may be sufficient to provide the desired degree of leakage, a plurality of grooves can be provided, for example spaced circumferentially around the sleeve. The or each groove can be aligned with the axis of the pipe or at an angle to the axis of the pipe. In one embodiment, for example, the or each groove can follow a helical path around the surface of the sleeve. As an alternative to grooves, the channels can be defined by means of protrusions, e.g. ribs, studs or bosses, on the inner surface of the sleeve which partially space the sealing means away from the surface of the sleeve.
Alternatively, or additionally, the sealing means itself can be configured to provide the leak path. For example, the sealing means can be provided with one or more grooves or passages therein or therethrough which permit the passage of fluid. Such grooves or passages can optionally be reinforced with a stiffer material such as a metal or a non-elastomeric plastics material in order to prevent the grooves or passages collapsing during compression.
The sealing means, sleeve and compression means are preferably configured such that in use, upon application of a compression force through the compression means, the axially outer portion of the sealing means is forced radially outwardly and into sealing engagement with the sleeve, whilst the axially inner portion of the sealing means is urged radially inwardly and into sealing engagement with the pipe.
In order to assist leakage of the fluid to compress the axially outer portion of the sealing means against the compression means, an annular void is typically formed between the axially inner portion of the sealing means and the sleeve, the annular void being in fluid communication with the leak path.
The end of the sleeve typically has an enlarged bore region within which is disposed the sealing means. The enlarged bore portion is usually linked to a relatively reduced bore region of the sleeve by an annular abutment surface. In order to assist compression, the annular abutment surface is preferably inclined radially outwardly (i.e flared) in the direction of the end of the sleeve.
A variety of differently shaped sealing means can be used but in one preferred embodiment, the sealing means takes the form of a multi-lobed sealing member, and in particular a sealing member which in cross section has two lobes. The two lobes can be of the same or different shape and can be, for example, of circular, ovoidal or polygonal shape. Where one or both lobes are polygonal in cross section, the polygon can be regular or irregular, particular examples being rectangular, pentagonal, hexagonal, heptagonal, octagonal, nonagonal and decagonal. Such polygonal lobes can have rounded or radiused edges. A most preferred sealing member of the invention has a cross sectional shape in the form of a filled figure of eight, a shape which can be regarded as functioning in a similar manner to a pair of O-rings joined together but has the advantage that the potential leakage between a pair of O-rings is avoided.
Alternatively, the sealing means can comprise a pair of O-rings. The two O-rings can advantageously be separated by a spacer ring which can, for example, have an inclined axially inner surface whereby compression of the axially inner O-ring by the spacer ring upon application of the compression means urges the said axially inner O-ring against the pipe. Alternatively or additionally, the spacer ring can have an inclined axially outer surface which assists in deforming the axially outer O-ring outwardly against the sleeve when the said axially outer O-ring is compressed by the compression means.
In a still further embodiment, the sealing means has a substantially trapezoidal cross section. In this embodiment, the trapezoidal shape may have a pair of axially aligned edges and a pair of radially aligned edges, the distance between the axially aligned edges being greater than the distance between the radially aligned edges. In order to assist in holding the sealing means against rotation, the radially aligned edges may be flattened. Alternatively, or additionally, the sleeve and the compression means can be provided with locating means for locating and holding one or more edges of the trapezoidal sealing member so as to prevent rotation. Such locating means can take the form of, for example, a groove or recess into which an edge of the sealing means can fit.
The compression means can take the form of a compression flange or compression collar which is drawn axially towards the sealing means for example by means of a screw thread or by the tightening of flange bolts. Such compression means can be entirely conventional.
In one embodiment, the compression means comprises an annular compression member which is arranged to encircle the pipe, means being provided for moving the annular compression member axially towards the sleeve and against the sealing means.
In a particular embodiment, the compression means can comprise an annular compression flange disposed axially outwardly of the annular compression member and a plurality of flange bolts to enable the annular compression flange to be tightened against the annular compression member thereby to compress the sealing means. Such an arrangement is particularly preferred when a separate gripping ring is employed as well as the sealing member. Thus the gripping member can be disposed axially between the compression flange and the compression member whilst the sealing means is disposed between the compression member and the sleeve. When a gripping ring is present, this can be arranged to be deformed radially inwardly against the pipe member by compression between the compression flange and compression member.
Alternatively, the separate compression member can be omitted and compression of the sealing means can be effected between a surface of the compression flange and the sleeve. Such an arrangement is particularly preferred when no separate gripping ring is present.
The pipe couplings of the invention can be used to couple together a pair of pipes, or can be used to couple a pipe to a non-pipe element, for example a tank or a pump. The term pipe as used herein includes pipes as such, and also pipe-like structures such as elbows, bends, tees, valves for example.
In a preferred embodiment, both ends of the sleeve are arranged to receive therein the respective ends of a pair of pipes. In particular, it is preferred that the sleeve, annular sealing means and compression means have substantially the same configuration at both ends of the sleeve.
In another aspect of the invention, there is provided a pipe joint comprising a pipe coupling as hereinbefore defined having a pipe disposed in the end of the sleeve thereof.
The invention will now be illustrated, but not limited, by reference to the particular embodiments shown in the accompanying drawings.